Mixtures of terminal olefins, commonly referred to as .alpha.-olefins, are made commercially by ethylene chain growth of aluminum alkyls followed by displacement. Such products are mainly .alpha.-olefins having the structure: EQU R--CH.sub.2 --CH.dbd.CH.sub.2
wherein R is an aliphatic hydrocarbon group. These are referred to as "vinyl olefins". A substantial portion of the .alpha.-olefins can be in the form of "vinylidene olefins" which have the structure: ##STR3## wherein both R groups are aliphatic hydrocarbon groups.
For many uses it is highly desirable to retain the olefin unsaturation in the terminal position. However, in making alkyl sulfonate surfactants by the known process of reacting an olefin with hydrogen sulfide in the presence of a Lewis Acid catalyst followed by oxidation with for example nitric oxide and oxygen to form sulfonic acid, it has been found that superior surfactant properties are achieved using internal olefins. Internal olefins can be made from .alpha.-olefins by isomerizing the olefin double bond from a terminal to an internal position. When this is done, using conventional isomerization catalyst such as alumina or silica/alumina, a major portion of the olefin groups of the vinylidene olefins are isomerized to the adjacent carbon-carbon bond forming what is termed "tri-substituted" internal olefins which have the structure: ##STR4## wherein each R is an aliphatic hydrocarbon group. Tri-substituted internal olefins are not as effective when converted to sulfonate surfactants as are the "di-substituted" internal olefins in which the olefin has the structure: EQU R--CH.dbd.CH--R
wherein each R is an aliphatic hydrocarbon group. Accordingly, a need exists for an isomerization process that will convert vinylidene olefins to mainly di-substituted internal olefins and minimize formation of tri-substituted internal olefins.
Iron carbonyl has been used to isomerize the double bond on certain olefins. Yardley et al, U.S. Pat. No. 4,338,173 describe the isomerization of an olefin double bond in the presence of iron carbonyl under ultraviolet light. The double bond migrates to the adjacent carbon-carbon bond. If this were applied to vinylidene olefins, one would expect the product to be a tri-substituted olefin.
Casey et al, J. Am. Chem. Soc., 95, Apr. 4, 1973, p. 2248-53, describe the isomerization of 3-ethyl-1-penetene in the presence of tri-iron dodecacarbonyl. The double bond migrates to the adjacent carbon-carbon bond forming 3-ethyl-2-pentene, a tri-substituted internal olefin. Similar results were obtained with 3-methyl-1-butene.
Bingham, et al, J. Chem. Soc., 14, 1974, p. 1521, report the isomerization of pent-1-ene in the presence of an iron carbonyl to form a cis-trans mixture of pent-2-ene. Chappell, et al, U.S. Pat. No. 3,398,205, describe the isomerization of cyclic diene using an iron carbonyl catalyst under carbon monoxide pressure. Kroll, U.S. Pat. No. 3,439,054, teach the use of a complex of iron carbonyl and tri-alkyl aluminum as a hydrogenation and isomerization catalyst. Contrary to what is taught by Chappell, et al, Kroll suggests that carbonyls alone will not isomerize cyclic dienes.
None of the prior art contains disclosure of the isomerization of a vinylidene olefin using an iron carbonyl catalyst and the prior art would predict that the product of such an isomerization if successful would form mainly tri-substituted internal olefins.